Hello Geoff,
I suspect that others may have more information than myself,and if you've already looked my apologies, but Joe Baughers site
http://joebaugher.com/usaf_serials/1930.html
has the XP-41 with NACA until 3 April 1942. I have contacted Joe in connection with the XP-41 at 10 ABS and he was unaware of this. It seems logical at least that if the XP-41 was used as a ground instructional airframe that it would be after this date.
Meanwhile on ebay here is a photo of the Curtiss XP-46 40-3053:
https://www.ebay.com/itm/26525668248...AAAOSwOMBhDcie
Regards,
Clint